Compound change gear transmissions of the type having one or more auxiliary sections connected in series with a main transmission section are well known in the prior art. Briefly, by utilizing main and auxiliary transmission sections connected in series, assuming proper sizing of the ratio steps, the total of available transmission ratios is equal to the product of the main and auxiliary section ratios. By way of example, at least in theory, a compound change gear transmission comprising a four (4) speed main section connected in series with a three (3) speed auxiliary section will provide twelve (4.times.3=12) available ratios.
Auxiliary transmission sections are of three general types: range type, splitter type or combined range/splitter type.
In compound transmissions having a range type auxiliary section, the ratio step or steps may be greater, equal or less than the total ratio coverage of the main transmission section and the main section is shifted progressively through its ratios in each range. Examples of compound transmissions having range type auxiliary sections may be seen by reference to U.S. Pat. Nos. 3,105,395; 2,637,222 and 2,637,221, the disclosures of which are hereby incorporated by reference.
In compound transmissions having a splitter type auxiliary section, the ratio steps of the splitter auxiliary section are less than the ratio steps of the main transmission section and each main section ratio is split, or subdivided, by the splitter section. Examples of compound change gear transmissions having splitter type auxiliary sections may be seen by reference to U.S. Pat. Nos. 4,290,515; 3,799,002; 4,440,037 and 4,527,447, the disclosures of which are hereby incorporated by reference.
In a combined range and splitter type auxiliary section, or sections, both range and splitter type ratios are provided allowing the main section to be progressively shifted through its ratios in at least two ranges and also allowing the main section ratios to be split in at least one range.
One example of a compound transmission having a single combined range/splitter type auxiliary section may be seen by reference to U.S. Pat. Nos. 3,283,613; 3,648,546, the disclosures of which are hereby incorporated by reference and to publication Small Scale Print No. 016-AD; Fuller Transmissions; Models RT-14613, RTO-14613, RTOO-14613, published March 1981 by Eaton Corporation, assignee of this invention, the disclosure of which is hereby incorporated by reference. Another example is the "Ecosplit" model of transmission sold by Zahnradfabrik Friedrichshafen Aktiengeseushaft of Friedrichshafen, Federal Republic of Germany which utilizes a separate splitter auxiliary section in front of, and a separate range auxiliary section behind, the main transmission section.
It should be noted that the terms main and auxiliary sections are relative and that if the designations of the main and auxiliary sections are reversed, the type of auxiliary section (either range or splitter) will also be reversed. In other words, given what is conventionally considered a four-speed main section with two-speed range type auxiliary section, if the normally designated auxiliary is considered the main section, the normally designated main section would be considered a four-speed splitter type auxiliary section therefor. By generally accepted transmission industry convention, and as used in this description of the invention, the main transmission section of a compound transmission is that section which contains the largest (or at least no less) number of forward speed ratios, which allows selection of a neutral position, which contains the reverse ratio(s) and/or which is shifted (in manual or semiautomatic transmissions) by manipulation of a shift bar or shift rail or shift shaft/shift finger assembly as opposed to master/slave valve/cylinder arrangements or the like.
A conventional auxiliary transmission section such as that disclosed in U.S. Pat. No. 4,754,665 includes an auxiliary section input shaft and an output shaft cooperably forming a mainshaft assembly, and an auxiliary countershaft assembly. The auxiliary transmission section includes three gear layers, combined range and splitter gearing and four distinct selectable auxiliary section ratios.